Apparatus and method for recognizing a tap gesture on a touch sensing device

ABSTRACT

Methods and apparatus include determine velocity of a detected presence in a first direction relative to a capacitive sensing surface, during a period of time, and determine velocity of the detected presence in a second direction relative to the capacitive sensing surface, during the period of time. Methods and apparatus detect a change in the determined velocity in the first direction at a first time, detect a change in the determined velocity in the second direction at a second time; and recognize a user command based on a difference between the first time and the second time.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.13/367,720, filed Feb. 7, 2012, now U.S. Pat. No. 8,610,686, issued Dec.17, 2013, which is a continuation of U.S. application Ser. No.11/395,674, filed Mar. 30, 2006, now U.S. Pat. No. 8,111,243, issuedFeb. 7, 2012, all of which are incorporated by reference herein in theirentirety.

TECHNICAL FIELD

This invention relates to the field of user interface devices and, inparticular, to touch-sensing devices.

BACKGROUND

Computing devices, such as notebook computers, personal data assistants(PDAs), and mobile handsets, have user interface devices, which are alsoknown as human interface device (HID). One user interface device thathas become more common is a touch-sensor pad. A basic notebooktouch-sensor pad emulates the function of a personal computer (PC)mouse. A touch-sensor pad is typically embedded into a PC notebook forbuilt-in portability. A touch-sensor pad replicates mouse x/y movementby using two defined axes which contain a collection of sensor elementsthat detect the position of a conductive object, such as finger. Mouseright/left button clicks can be replicated by two mechanical buttons,located in the vicinity of the touchpad, or by tapping commands on thetouch-sensor pad itself. The touch-sensor pad provides a user interfacedevice for performing such functions as positioning a cursor, orselecting an item on a display. These touch-sensor pads can includemulti-dimensional sensor arrays. The sensor array may be onedimensional, detecting movement in one axis. The sensor array may alsobe two dimensional, detecting movements in two axes.

FIG. 1A illustrates a conventional touch-sensor pad. The touch-sensorpad 100 includes a sensing surface 101 on which a conductive object maybe used to position a cursor in the x- and y-axes. Touch-sensor pad 100may also include two buttons, left and right buttons 102 and 103,respectively. These buttons are typically mechanical buttons, andoperate much like a left and right button on a mouse. These buttonspermit a user to select items on a display or send other commands to thecomputing device.

In addition to detecting motion of the conductive object in one or twoaxes to control cursor movement, these conventional touch-sensor padshave been designed to recognize gesture features. One conventionaltouch-sensor pad includes methods for recognizing gestures made by aconductive object on a touch-sensor pad, as taught by U.S. Pat. No.6,380,931 to Gillespie et al. This conventional touch-sensor padrecognizes tapping, pushing, hopping, and zigzag gestures by analyzingthe position, pressure, and movement of the conductive object on thesensor pad during the time of a suspected gesture, and sends signals toa host indicating the occurrence of these gestures.

This conventional touch-sensor pad includes a capacitive positionsensing system, which determines the position of the conductive object,such as a finger, that is proximate to or touching a sensing surface.This conventional touch-sensor pad also obtains the finger pressure bysumming the capacitances measured on sense lines. A finger is present ifthe pressure exceeds a suitable threshold value. The basic “tap” gestureis a quick tap of the finger on the pad. Such a tap, of short duration,involving little or no X or Y finger motion during the tap, is presentedto the host as a brief click of the mouse button. If a multi-buttonmouse is simulated, the tap gesture may simulate a click of the“primary” mouse button, or the button to be simulated may beuser-selectable using a shift key, control panel, or other known means.Two taps in rapid succession are presented to the host as a double clickof the button. In general, multiple taps translate into multiple clicks.

In addition, because it is impossible to tell whether a finger strokewill be a valid tap while the finger is still down (as opposed to acursor motion), this conventional touch-sensor pad, does not report abutton click until the finger is lifted. This delay is not generallynoticeable to the user since taps by definition are very brief strokes.

FIG. 1B illustrates a graph of the capacitance over time of theconventional touch-sensor pad described above. Graph 104 includes apressure threshold, Z_(tap) 109, and a threshold time, T_(tap) 107.Z_(tap) 109 is the minimum pressure to detect a tapping finger. T_(tap)107 is the maximum amount of time that the finger is in contact with thetouch-sensor pad in order to qualify as a tap gesture. Line 105illustrates the capacitance over time of finger as it comes into contactwith the touch-sensor pad, and as the finger releases from thetouch-sensor pad. Line 105 crosses the pressure threshold Z_(tap) 109 intwo cross-points, points 110 and 111. The time (T) 106 between the twocross-points 110 and 111 is less than the threshold time T_(tap) 107,and accordingly, is recognized as a tap gesture. In other words, usingthis method, if the amount of time the conductive object is present onthe touch-sensor pad (i.e., above the pressure threshold Ztap 109) isless than the reference amount of time, T_(tap) 107, then a tap gesturewill be recognized.

One problem with this conventional method for recognizing a tap gestureis that it requires measuring the time of the presence of the conductiveobject only above the minimum pressure threshold. This method couldpotentially lead to mistaking “slow touching” of the conductive objecton the touch-sensor pad with a tap gesture. “Slow touching” 108 isillustrated in FIG. 1B. Slow touching 108 also crosses the pressurethreshold 109 at two cross-points 112 and 113. The time measured betweenthese two cross-points is less than the time threshold Ttap 107, andaccordingly, is recognized as a tap gesture, when in fact the user isnot tapping the touch-sensor pad, but is slowly touching thetouch-sensor pad.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example, and not by wayof limitation, in the figures of the accompanying drawings.

FIG. 1A illustrates a conventional touch-sensor pad.

FIG. 1B illustrates a graph of the capacitance over time of theconventional touch-sensor pad described above.

FIG. 2 illustrates a block diagram of one embodiment of an electronicsystem having a processing device for recognizing a tap gesture.

FIG. 3A illustrates a varying switch capacitance.

FIG. 3B illustrates one embodiment of a relaxation oscillator.

FIG. 4 illustrates a block diagram of one embodiment of a capacitancesensor including a relaxation oscillator and digital counter.

FIG. 5A illustrates a top-side view of one embodiment of a sensor arrayhaving a plurality of sensor elements for detecting a presence of aconductive object on the sensor array of a touch-sensor pad.

FIG. 5B illustrates a top-side view of one embodiment of a sensor arrayhaving a plurality of sensor elements for detecting a presence of aconductive object on the sensor array of a touch-sensor slider

FIG. 5C illustrates a top-side view of one embodiment of a two-layertouch-sensor pad.

FIG. 5D illustrates a side view of one embodiment of the two-layertouch-sensor pad of FIG. 5C.

FIG. 6 illustrates a graph of one embodiment of a velocity of a presenceof a finger on a sensing device

FIG. 7A illustrates a graph of one embodiment of a differential of thecapacitance over time on a sensing device.

FIG. 7B illustrates a graph of one embodiment of a peak in thedifferential of the capacitance on the sensing device.

FIG. 8A illustrates a graph of one embodiment of an integration of thecapacitance over time on a sensing device.

FIG. 8B illustrates a graph of another embodiment of an integration ofthe capacitance over time on a sensing device.

FIG. 9A illustrates a flowchart of one embodiment of a method forrecognizing a tap gesture on a sensing device.

FIG. 9B illustrates a flowchart of another exemplary embodiment of amethod for recognizing a tap gesture on a sensing device.

DETAILED DESCRIPTION

Described herein is a method and apparatus for recognizing a tap gestureon a touch sensing device, such as a touch-sensor pad, touch-sensorslider, or a touch-sensor button. The following description sets forthnumerous specific details such as examples of specific systems,components, methods, and so forth, in order to provide a goodunderstanding of several embodiments of the present invention. It willbe apparent to one skilled in the art, however, that at least someembodiments of the present invention may be practiced without thesespecific details. In other instances, well-known components or methodsare not described in detail or are presented in simple block diagramformat in order to avoid unnecessarily obscuring the present invention.Thus, the specific details set forth are merely exemplary. Particularimplementations may vary from these exemplary details and still becontemplated to be within the spirit and scope of the present invention.

Embodiments of a method and apparatus are described to recognize a tapgesture on a sensing device. In one embodiment, the method may includedetecting a presence of a conductive object on a sensing device,determining a velocity of the detected presence of the conductiveobject, and recognizing a tap gesture based on the velocity. Determiningthe velocity may include determining a capacitance of the conductiveobject on the sensing device over time, and determining a differentialof the capacitance over the time. The differential is representative ofthe velocity of the presence, and the tap gesture is recognized based onthe determined differential of the capacitance. The apparatus mayinclude a sensing device having a plurality of sensor elements to detecta presence of a conductive object on the sensing device, and aprocessing device coupled to the sensing device. The processing deviceis configured to determine a velocity of the detected presence of theconductive object, and to recognize a tap gesture based on the velocity.In one embodiment, the velocity of the presence of the conductive objectis the rate of change or differential of the capacitance on the sensingdevice.

The differential of the capacitance over time naturally captures therising and falling edge, which represents the on- and off-actions of thetap gesture, respectively. Moreover, the shapes of the derived peaksyield more information. For example, a snappy action gives a sharp peak,while a slow touching action give rise to a mild peak, which can beeasily quantified by the sharpness factor, Q, which is characteristic ofthe sharpness of the peak. In other words, the sharpness of the peakdepends on the velocity of the presence of the conductive object, as theconductive object approaches and departs from the sensing device. Thepresence of the conductive object is when the conductive object is in oris substantially in contact with the sensing device. The sharpnessfactor Q may be determined using the height and width of the peak. Thetime distance between the 2 peaks (e.g., on- and off-actions) isevaluated and used as criteria, together with the Q values of the 2peaks, to recognize a tap gesture. Using the differential algorithm,unlike the conventional touch-sensor pads, the embodiments describedherein can distinguish between tap gestures and slow touching.

FIG. 2 illustrates a block diagram of one embodiment of an electronicsystem having a processing device for recognizing a tap gesture.Electronic system 200 includes processing device 210, touch-sensor pad220, touch-sensor slider 230, touch-sensor buttons 240, host processor250, embedded controller 260, and non-capacitance sensor elements 270.The processing device 210 may include analog and/or digital generalpurpose input/output (“GPIO”) ports 207. GPIO ports 207 may beprogrammable. GPIO ports 207 may be coupled to a ProgrammableInterconnect and Logic (“PIL”), which acts as an interconnect betweenGPIO ports 207 and a digital block array of the processing device 210(not illustrated). The digital block array may be configured toimplement a variety of digital logic circuits (e.g., DAC, digitalfilters, digital control systems, etc.) using, in one embodiment,configurable user modules (“UMs”). The digital block array may becoupled to a system bus. Processing device 210 may also include memory,such as random access memory (RAM) 205 and program flash 204. RAM 205may be static RAM (SRAM), and program flash 204 may be a non-volatilestorage, which may be used to store firmware (e.g., control algorithmsexecutable by processing core 202 to implement operations describedherein). Processing device 210 may also include a memory controller unit(MCU) 203 coupled to memory and the processing core 202.

The processing device 210 may also include an analog block array (notillustrated). The analog block array is also coupled to the system bus.Analog block array also may be configured to implement a variety ofanalog circuits (e.g., ADC, analog filters, etc.) using configurableUMs. The analog block array may also be coupled to the GPIO 207.

As illustrated, capacitance sensor 201 may be integrated into processingdevice 210. Capacitance sensor 201 may include analog I/O for couplingto an external component, such as touch-sensor pad 220, touch-sensorslider 230, touch-sensor buttons 240, and/or other devices. Capacitancesensor 201 and processing device 202 are described in more detail below.

It should be noted that the embodiments described herein are not limitedto touch-sensor pads for notebook implementations, but can be used inother capacitive sensing implementations, for example, the sensingdevice may be a touch-slider 230, or a touch-sensor 240 (e.g.,capacitance sensing button). Similarly, the operations described hereinare not limited to notebook cursor operations, but can include otheroperations, such as lighting control (dimmer), volume control, graphicequalizer control, speed control, or other control operations requiringgradual adjustments. It should also be noted that these embodiments ofcapacitive sensing implementations may be used in conjunction withnon-capacitive sensing elements, including but not limited to pickbuttons, sliders (ex. display brightness and contrast), scroll-wheels,multi-media control (ex. volume, track advance, etc) handwritingrecognition and numeric keypad operation.

In one embodiment, the electronic system 200 includes a touch-sensor pad220 coupled to the processing device 210 via bus 221. Touch-sensor pad220 may include a multi-dimension sensor array. The multi-dimensionsensor array comprises a plurality of sensor elements, organized as rowsand columns. In another embodiment, the electronic system 200 includes atouch-sensor slider 230 coupled to the processing device 210 via bus231. Touch-sensor slider 230 may include a single-dimension sensorarray. The single-dimension sensor array comprises a plurality of sensorelements, organized as rows, or alternatively, as columns. In anotherembodiment, the electronic system 200 includes a touch-sensor button 240coupled to the processing device 210 via bus 241. Touch-sensor button240 may include a single-dimension or multi-dimension sensor array. Thesingle- or multi-dimension sensor array comprises a plurality of sensorelements. For a touch-sensor button, the plurality of sensor elementsmay be coupled together to detect a presence of a conductive object overthe entire surface of the sensing device. Capacitance sensor elementsmay be used as non-contact switches. These switches, when protected byan insulating layer, offer resistance to severe environments.

The electronic system 200 may include any combination of one or more ofthe touch-sensor pad 220, touch-sensor slider 230, and/or touch-sensorbutton 240. In another embodiment, the electronic system 200 may alsoinclude non-capacitance sensor elements 270 coupled to the processingdevice 210 via bus 271. The non-capacitance sensor elements 270 mayinclude buttons, light emitting diodes (LEDs), and other user interfacedevices, such as a mouse, a keyboard, or other functional keys that donot require capacitance sensing. In one embodiment, buses 271, 241, 231,and 221 may be a single bus. Alternatively, these buses may beconfigured into any combination of one or more separate buses.

The processing device may also provide value-add functionality such askeyboard control integration, LEDs, battery charger and general purposeI/O, as illustrated as non-capacitance sensor elements 270.Non-capacitance sensor elements 270 are coupled to the GPIO 207.

Processing device 210 may include internal oscillator/clocks 206, andcommunication block 208. The oscillator/clocks block 206 provides clocksignals to one or more of the components of processing device 210.Communication block 208 may be used to communicate with an externalcomponent, such as a host processor 250, via host interface (I/F) line251. Alternatively, processing block 210 may also be coupled to embeddedcontroller 260 to communicate with the external components, such as host250. Interfacing to the host 250 can be through various methods. In oneexemplary embodiment, interfacing with the host 250 may be done using astandard PS/2 interface to connect to an embedded controller 260, whichin turn sends data to the host 250 via low pin count (LPC) interface. Insome instances, it may be beneficial for the processing device 210 to doboth touch-sensor pad and keyboard control operations, thereby freeingup the embedded controller 260 for other housekeeping functions. Inanother exemplary embodiment, interfacing may be done using a universalserial bus (USB) interface directly coupled to the host 250 via hostinterface line 251. Alternatively, the processing device 210 maycommunicate to external components, such as the host 250 using industrystandard interfaces, such as USB, PS/2, inter-integrated circuit (I2C)bus, or system packet interface (SPI). The embedded controller 260and/or embedded controller 260 may be coupled to the processing device210 with a ribbon or flex cable from an assembly, which houses thetouch-sensor pad and processing device.

In one embodiment, the processing device 210 is configured tocommunicate with the embedded controller 260 or the host 250 to senddata. The data may be a command or alternatively a signal. In anexemplary embodiment, the electronic system 200 may operate in bothstandard-mouse compatible and enhanced modes. The standard-mousecompatible mode utilizes the HID class drivers already built into theOperating System (OS) software of host 250. These drivers enable theprocessing device 210 and sensing device to operate as a standard cursorcontrol user interface device, such as a two-button PS/2 mouse. Theenhanced mode may enable additional features such as scrolling(reporting absolute position) or disabling the sensing device, such aswhen a mouse is plugged into the notebook. Alternatively, the processingdevice 210 may be configured to communicate with the embedded controller260 or the host 250, using non-OS drivers, such as dedicatedtouch-sensor pad drivers, or other drivers known by those of ordinaryskill in the art.

In other words, the processing device 210 may operate to communicatedata (e.g., commands or signals) using hardware, software, and/orfirmware, and the data may be communicated directly to the processingdevice of the host 250, such as a host processor, or alternatively, maybe communicated to the host 250 via drivers of the host 250, such as OSdrivers, or other non-OS drivers. It should also be noted that the host250 may directly communicate with the processing device 210 via hostinterface 251.

In one embodiment, the data sent to the host 250 from the processingdevice 210 includes click, double-click, movement of the cursor,scroll-up, scroll-down, scroll-left, scroll-right, step Back, and stepForward. Alternatively, other user interface device commands may becommunicated to the host 250 from the processing device 210. Thesecommands may be based on gestures occurring on the sensing device thatare recognized by the processing device, such as tap, push, hop, andzigzag gestures. Alternatively, other commands may be recognized.Similarly, signals may be sent that indicate the recognition of theseoperations.

In particular, a tap gesture, for example, may be when the finger (e.g.,conductive object) is on the sensing device for less than a thresholdtime. If the time the finger is placed on the touchpad is greater thanthe threshold time it may be considered to be a movement of the cursor,in the x- or y-axes. Scroll-up, scroll-down, scroll-left, andscroll-right, step back, and step-forward may be detected when theabsolute position of the conductive object is within a pre-defined area,and movement of the conductive object is detected.

Processing device 210 may reside on a common carrier substrate such as,for example, an integrated circuit (IC) die substrate, a multi-chipmodule substrate, or the like. Alternatively, the components ofprocessing device 210 may be one or more separate integrated circuitsand/or discrete components. In one exemplary embodiment, processingdevice 210 may be a Programmable System on a Chip (PSoC™) processingdevice, manufactured by Cypress Semiconductor Corporation, San Jose,Calif. Alternatively, processing device 210 may be other one or moreprocessing devices known by those of ordinary skill in the art, such asa microprocessor or central processing unit, a controller,special-purpose processor, digital signal processor (DSP), anapplication specific integrated circuit (ASIC), a field programmablegate array (FPGA), or the like. In an alternative embodiment, forexample, the processing device may be a network processor havingmultiple processors including a core unit and multiple microengines.Additionally, the processing device may include any combination ofgeneral-purpose processing device(s) and special-purpose processingdevice(s).

Capacitance sensor 201 may be integrated into the IC of the processingdevice 210, or alternatively, in a separate IC. Alternatively,descriptions of capacitance sensor 201 may be generated and compiled forincorporation into other integrated circuits. For example, behaviorallevel code describing capacitance sensor 201, or portions thereof, maybe generated using a hardware descriptive language, such as VHDL orVerilog, and stored to a machine-accessible medium (e.g., CD-ROM, harddisk, floppy disk, etc.). Furthermore, the behavioral level code can becompiled into register transfer level (“RTL”) code, a netlist, or even acircuit layout and stored to a machine-accessible medium. The behaviorallevel code, the RTL code, the netlist, and the circuit layout allrepresent various levels of abstraction to describe capacitance sensor201.

It should be noted that the components of electronic system 200 mayinclude all the components described above. Alternatively, electronicsystem 200 may include only some of the components described above.

In one embodiment, electronic system 200 may be used in a notebookcomputer. Alternatively, the electronic device may be used in otherapplications, such as a mobile handset, a personal data assistant (PDA),a keyboard, a television, a remote control, a monitor, a handheldmulti-media device, a handheld video player, a handheld gaming device,or a control panel.

In one embodiment, capacitance sensor 201 may be a capacitive switchrelaxation oscillator (CSR). The CSR may have an array of capacitivetouch switches using a current-programmable relaxation oscillator, ananalog multiplexer, digital counting functions, and high-level softwareroutines to compensate for environmental and physical switch variations.The switch array may include combinations of independent switches,sliding switches (e.g., touch-sensor slider), and touch-sensor padsimplemented as a pair of orthogonal sliding switches. The CSR mayinclude physical, electrical, and software components. The physicalcomponent may include the physical switch itself, typically a patternconstructed on a printed circuit board (PCB) with an insulating cover, aflexible membrane, or a transparent overlay. The electrical componentmay include an oscillator or other means to convert a changedcapacitance into a measured signal. The electrical component may alsoinclude a counter or timer to measure the oscillator output. Thesoftware component may include detection and compensation softwarealgorithms to convert the count value into a switch detection decision.For example, in the case of slide switches or X-Y touch-sensor pads, acalculation for finding position of the conductive object to greaterresolution than the physical pitch of the switches may be used.

It should be noted that there are various known methods for measuringcapacitance. Although the embodiments described herein are describedusing a relaxation oscillator, the present embodiments are not limitedto using relaxation oscillators, but may include other methods, such ascurrent versus voltage phase shift measurement, resistor-capacitorcharge timing, capacitive bridge divider or, charge transfer.

The current versus voltage phase shift measurement may include drivingthe capacitance through a fixed-value resistor to yield voltage andcurrent waveforms that are out of phase by a predictable amount. Thedrive frequency can be adjusted to keep the phase measurement in areadily measured range. The resistor-capacitor charge timing may includecharging the capacitor through a fixed resistor and measuring timing onthe voltage ramp. Small capacitor values may require very largeresistors for reasonable timing. The capacitive bridge divider mayinclude driving the capacitor under test through a fixed referencecapacitor. The reference capacitor and the capacitor under test form avoltage divider. The voltage signal is recovered with a synchronousdemodulator, which may be done in the processing device 210. The chargetransfer may be conceptually similar to an R-C charging circuit. In thismethod, C_(P) is the capacitance being sensed. C_(SUM) is the summingcapacitor, into which charge is transferred on successive cycles. At thestart of the measurement cycle, the voltage on C_(SUM) is reset. Thevoltage on C_(SUM) increases exponentially (and only slightly) with eachclock cycle. The time for this voltage to reach a specific threshold ismeasured with a counter. Additional details regarding these alternativeembodiments have not been included so as to not obscure the presentembodiments, and because these alternative embodiments for measuringcapacitance are known by those of ordinary skill in the art.

FIG. 3A illustrates a varying switch capacitance. In its basic form, acapacitive switch 300 is a pair of adjacent plates 301 and 302. There isa small edge-to-edge capacitance Cp, but the intent of switch layout isto minimize the base capacitance Cp between these plates. When aconductive object 303 (e.g., finger) is placed in proximity to the twoplate 301 and 302, there is a capacitance 2*Cf between one electrode 301and the conductive object 303 and a similar capacitance 2*Cf between theconductive object 303 and the other electrode 302. The capacitancebetween one electrode 301 and the conductive object 303 and back to theother electrode 302 adds in parallel to the base capacitance Cp betweenthe plates 301 and 302, resulting in a change of capacitance Cf.Capacitive switch 300 may be used in a capacitance switch array. Thecapacitance switch array is a set of capacitors where one side of eachis grounded. Thus, the active capacitor (as represented in FIG. 3B ascapacitor 351) has only one accessible side. The presence of theconductive object 303 increases the capacitance (Cp+Cf) of the switch300 to ground. Determining switch activation is then a matter ofmeasuring change in the capacitance (Cf). Switch 300 is also known as agrounded variable capacitor. In one exemplary embodiment, Cf may rangefrom approximately 10-30 picofarads (pF). Alternatively, other rangesmay be used.

The conductive object in this case is a finger, alternatively, thistechnique may be applied to any conductive object, for example, aconductive door switch, position sensor, or conductive pen in a stylustracking system.

FIG. 3B illustrates one embodiment of a relaxation oscillator. Therelaxation oscillator 350 is formed by the capacitance to be measured oncapacitor 351, a charging current source 352, a comparator 353, and areset switch 354. It should be noted that capacitor 351 isrepresentative of the capacitance measured on a sensor element of asensor array. The relaxation oscillator is coupled to drive a chargingcurrent (Ic) 357 in a single direction onto a device under test (“DUT”)capacitor, capacitor 351. As the charging current piles charge onto thecapacitor 351, the voltage across the capacitor increases with time as afunction of Ic 357 and its capacitance C. Equation (1) describes therelation between current, capacitance, voltage and time for a chargingcapacitor.CdV=I_(c)dt  (1)

The relaxation oscillator begins by charging the capacitor 351 from aground potential or zero voltage and continues to pile charge on thecapacitor 351 at a fixed charging current Ic 357 until the voltageacross the capacitor 351 at node 355 reaches a reference voltage orthreshold voltage, V_(TH) 355. At V_(TH) 355, the relaxation oscillatorallows the accumulated charge at node 355 to discharge (e.g., thecapacitor 351 to “relax” back to the ground potential) and then theprocess repeats itself. In particular, the output of comparator 353asserts a clock signal F_(OUT) 356 (e.g., F_(OUT) 356 goes high), whichenables the reset switch 354. This resets the voltage on the capacitorat node 355 to ground and the charge cycle starts again. The relaxationoscillator outputs a relaxation oscillator clock signal (F_(OUT) 356)having a frequency (f_(RO)) dependent upon capacitance C of thecapacitor 351 and charging current Ic 357.

The comparator trip time of the comparator 353 and reset switch 354 adda fixed delay. The output of the comparator 353 is synchronized with areference system clock to guarantee that the comparator reset time islong enough to completely reset the charging voltage on capacitor 355.This sets a practical upper limit to the operating frequency. Forexample, if capacitance C of the capacitor 351 changes, then f_(RO) willchange proportionally according to Equation (1). By comparing f_(RO) ofF_(OUT) 356 against the frequency (f_(REF)) of a known reference systemclock signal (REF CLK), the change in capacitance ΔC can be measured.Accordingly, equations (2) and (3) below describe that a change infrequency between F_(OUT) 356 and REF CLK is proportional to a change incapacitance of the capacitor 351.ΔC∞Δf, where  (2)Δf=f _(RO) −F _(REF).  (3)

In one embodiment, a frequency comparator may be coupled to receiverelaxation oscillator clock signal (F_(OUT) 356) and REF CLK, comparetheir frequencies f_(RO) and f_(REF), respectively, and output a signalindicative of the difference Δf between these frequencies. By monitoringΔf one can determine whether the capacitance of the capacitor 351 haschanged.

In one exemplary embodiment, the relaxation oscillator 350 may be builtusing a 555 timer to implement the comparator 353 and reset switch 354.Alternatively, the relaxation oscillator 350 may be built using othercircuiting. Relaxation oscillators are known in by those of ordinaryskill in the art, and accordingly, additional details regarding theiroperation have not been included so as to not obscure the presentembodiments.

FIG. 4 illustrates a block diagram of one embodiment of a capacitancesensor including a relaxation oscillator and digital counter.Capacitance sensor 201 of FIG. 4 includes a sensor array 410 (also knownas a switch array), relaxation oscillator 350, and a digital counter420. Sensor array 410 includes a plurality of sensor elements355(1)-355(N), where N is a positive integer value that represents thenumber of rows (or alternatively columns) of the sensor array 410. Eachsensor element is represented as a capacitor, as previously describedwith respect to FIG. 3B. The sensor array 410 is coupled to relaxationoscillator 350 via an analog bus 401 having a plurality of pins401(1)-401(N). In one embodiment, the sensor array 410 may be asingle-dimension sensor array including the sensor elements355(1)-355(N), where N is a positive integer value that represents thenumber of sensor elements of the single-dimension sensor array. Thesingle-dimension sensor array 410 provides output data to the analog bus401 of the processing device 210 (e.g., via lines 231). Alternatively,the sensor array 410 may be a multi-dimension sensor array including thesensor elements 355(1)-355(N), where N is a positive integer value thatrepresents the number of sensor elements of the multi-dimension sensorarray. The multi-dimension sensor array 410 provides output data to theanalog bus 401 of the processing device 210 (e.g., via bus 221).

Relaxation oscillator 350 of FIG. 4 includes all the componentsdescribed with respect to FIG. 3B, and a selection circuit 430. Theselection circuit 430 is coupled to the plurality of sensor elements355(1)-355(N), the reset switch 354, the current source 352, and thecomparator 353. Selection circuit 430 may be used to allow therelaxation oscillator 350 to measure capacitance on multiple sensorelements (e.g., rows or columns). The selection circuit 430 may beconfigured to sequentially select a sensor element of the plurality ofsensor elements to provide the charge current and to measure thecapacitance of each sensor element. In one exemplary embodiment, theselection circuit 430 is a multiplexer array of the relaxationoscillator 350. Alternatively, selection circuit may be other circuitryoutside the relaxation oscillator 350, or even outside the capacitancesensor 201 to select the sensor element to be measured. Capacitancesensor 201 may include one relaxation oscillator and digital counter forthe plurality of sensor elements of the sensor array. Alternatively,capacitance sensor 201 may include multiple relaxation oscillators anddigital counters to measure capacitance on the plurality of sensorelements of the sensor array. The multiplexer array may also be used toground the sensor elements that are not being measured. This may be donein conjunction with a dedicated pin in the GP10 port 207.

In another embodiment, the capacitance sensor 201 may be configured tosimultaneously scan the sensor elements, as opposed to being configuredto sequentially scan the sensor elements as described above. Forexample, the sensing device may include a sensor array having aplurality of rows and columns. The rows may be scanned simultaneously,and the columns may be scanned simultaneously.

In one exemplary embodiment, the voltages on all of the rows of thesensor array are simultaneously moved, while the voltages of the columnsare held at a constant voltage, with the complete set of sampled pointssimultaneously giving a profile of the conductive object in a firstdimension. Next, the voltages on all of the rows are held at a constantvoltage, while the voltages on all the rows are simultaneously moved, toobtain a complete set of sampled points simultaneously giving a profileof the conductive object in the other dimension.

In another exemplary embodiment, the voltages on all of the rows of thesensor array are simultaneously moved in a positive direction, while thevoltages of the columns are moved in a negative direction. Next, thevoltages on all of the rows of the sensor array are simultaneously movedin a negative direction, while the voltages of the columns are moved ina positive direction. This technique doubles the effect of anytranscapacitance between the two dimensions, or conversely, halves theeffect of any parasitic capacitance to the ground. In both methods, thecapacitive information from the sensing process provides a profile ofthe presence of the conductive object to the sensing device in eachdimension. Alternatively, other methods for scanning known by those ofordinary skill in the art may be used to scan the sensing device.

Digital counter 420 is coupled to the output of the relaxationoscillator 350. Digital counter 420 receives the relaxation oscillatoroutput signal 356 (F_(OUT)). Digital counter 420 is configured to countat least one of a frequency or a period of the relaxation oscillatoroutput received from the relaxation oscillator.

As previously described with respect to the relaxation oscillator 350,when a finger or conductive object is placed on the switch, thecapacitance increases from Cp to Cp+Cf so the relaxation oscillatoroutput signal 356 (F_(OUT)) decreases. The relaxation oscillator outputsignal 356 (F_(OUT)) is fed to the digital counter 420 for measurement.There are two methods for counting the relaxation oscillator outputsignal 356, frequency measurement and period measurement. In oneembodiment, the digital counter 420 may include two multiplexers 423 and424. Multiplexers 423 and 424 are configured to select the inputs forthe PWM 421 and the timer 422 for the two measurement methods, frequencyand period measurement methods. Alternatively, other selection circuitsmay be used to select the inputs for the PWM 421 and the time 422. Inanother embodiment, multiplexers 423 and 424 are not included in thedigital counter, for example, the digital counter 420 may be configuredin one, or the other, measurement configuration.

In the frequency measurement method, the relaxation oscillator outputsignal 356 is counted for a fixed period of time. The counter 422 isread to obtain the number of counts during the gate time. This methodworks well at low frequencies where the oscillator reset time is smallcompared to the oscillator period. A pulse width modulator (PWM) 441 isclocked for a fixed period by a derivative of the system clock, VC3 426(which is a divider from the 24 MHz system clock 425). Pulse widthmodulation is a modulation technique that generates variable-lengthpulses to represent the amplitude of an analog input signal; in thiscase VC3 426. The output of PWM 421 enables timer 422 (e.g., 16-bit).The relaxation oscillator output signal 356 clocks the timer 422. Thetimer 422 is reset at the start of the sequence, and the count value isread out at the end of the gate period.

In the period measurement method, the relaxation oscillator outputsignal 356 gates a counter 422, which is clocked by the system clock 425(e.g., 24 MHz). In order to improve sensitivity and resolution, multipleperiods of the oscillator are counted with the PWM 421. The output ofPWM 421 is used to gate the timer 422. In this method, the relaxationoscillator output signal 356 drives the clock input of PWM 421. Aspreviously described, pulse width modulation is a modulation techniquethat generates variable-length pulses to represent the amplitude of ananalog input signal; in this case the relaxation oscillator outputsignal 356. The output of the PWM 421 enables a timer 422 (e.g.,16-bit), which is clocked at the system clock frequency 425 (e.g., 24MHz). When the output of PWM 421 is asserted (e.g., goes high), thecount starts by releasing the capture control. When the terminal countof the PWM 421 is reached, the capture signal is asserted (e.g., goeshigh), stopping the count and setting the PWM's interrupt. The timervalue is read in this interrupt. The relaxation oscillator 350 isindexed to the next switch (e.g., capacitor 351(2)) to be measured andthe count sequence is started again.

The two counting methods may have equivalent performance in sensitivityand signal-to-noise ratio (SNR). The period measurement method may havea slightly faster data acquisition rate, but this rate is dependent onsoftware load and the values of the switch capacitances. The frequencymeasurement method has a fixed-switch data acquisition rate.

The length of the counter 422 and the detection time required for theswitch are determined by sensitivity requirements. Small changes in thecapacitance on capacitor 351 result in small changes in frequency. Inorder to find these small changes, it may be necessary to count for aconsiderable time.

At startup (or boot) the switches (e.g., capacitors 351(1)-(N)) arescanned and the count values for each switch with no actuation arestored as a baseline array (Cp). The presence of a finger on the switchis determined by the difference in counts between a stored value for noswitch actuation and the acquired value with switch actuation, referredto here as Δn. The sensitivity of a single switch is approximately:

$\begin{matrix}{\frac{\Delta\; n}{n} = \frac{C\; f}{C\; p}} & (4)\end{matrix}$

The value of Δn should be large enough for reasonable resolution andclear indication of switch actuation. This drives switch constructiondecisions.

Cf should be as large a fraction of Cp as possible. In one exemplaryembodiment, the fraction of Cf/Cp ranges between approximately 0.01 toapproximately 2.0. Alternatively, other fractions may be used for Cf/Cp.Since Cf is determined by finger area and distance from the finger tothe switch's conductive traces (through the over-lying insulator), thebaseline capacitance Cp should be minimized. The baseline capacitance Cpincludes the capacitance of the switch pad plus any parasitics,including routing and chip pin capacitance.

In switch array applications, variations in sensitivity should beminimized. If there are large differences in Δn, one switch may actuateat 1.0 cm, while another may not actuate until direct contact. Thispresents a non-ideal user interface device. There are numerous methodsfor balancing the sensitivity. These may include precisely matchingon-board capacitance with PC trace length modification, adding balancecapacitors on each switch's PC board trace, and/or adapting acalibration factor to each switch to be applied each time the switch istested.

In one embodiment, the PCB design may be adapted to minimizecapacitance, including thicker PCBs where possible. In one exemplaryembodiment, a 0.062 inch thick PCB is used. Alternatively, otherthicknesses may be used, for example, a 0.015 inch thick PCB.

It should be noted that the count window should be long enough for Δn tobe a “significant number.” In one embodiment, the “significant number”can be as little as 10, or alternatively, as much as several hundred. Inone exemplary embodiment, where Cf is 1.0% of Cp (a typical “weak”switch), and where the switch threshold is set at a count value of 20, nis found to be:

$\begin{matrix}{n = {{\Delta\;{n \cdot \frac{C\; f}{C\; p}}} = 2000}} & (5)\end{matrix}$

Adding some margin to yield 2500 counts, and running the frequencymeasurement method at 1.0 MHz, the detection time for the switch is 4microseconds. In the frequency measurement method, the frequencydifference between a switch with and without actuation (i.e., CP+CF vs.CP) is approximately:

$\begin{matrix}{{\Delta\; n} = {\frac{t_{count} \cdot i_{c}}{V_{T\; H}}\frac{C\; f}{C\; p^{2}}}} & (6)\end{matrix}$

This shows that the sensitivity variation between one channel andanother is a function of the square of the difference in the twochannels' static capacitances. This sensitivity difference can becompensated using routines in the high-level Application ProgrammingInterfaces (APIs).

In the period measurement method, the count difference between a switchwith and without actuation (i.e., CP+CF vs. CP) is approximately:

$\begin{matrix}{{\Delta\; n} = {N_{Periods} \cdot \frac{C\;{f \cdot V_{T\; H}}}{i_{c}} \cdot f_{SysClk}}} & (7)\end{matrix}$

The charge currents are typically lower and the period is longer toincrease sensitivity, or the number of periods for which f_(SysClk) iscounted can be increased. In either method, by matching the static(parasitic) capacitances Cp of the individual switches, therepeatability of detection increases, making all switches work at thesame difference. Compensation for this variation can be done in softwareat runtime. The compensation algorithms for both the frequency methodand period method may be included in the high-level APIs.

Some implementations of this circuit use a current source programmed bya fixed-resistor value. If the range of capacitance to be measuredchanges, external components, (i.e., the resistor) should be adjusted.

Using the multiplexer array 430, multiple sensor elements may besequentially scanned to provide current to and measure the capacitancefrom the capacitors (e.g., sensor elements), as previously described. Inother words, while one sensor element is being measured, the remainingsensor elements are grounded using the GPIO port 207. This drive andmultiplex arrangement bypasses the existing GPIO to connect the selectedpin to an internal analog multiplexer (mux) bus. The capacitor chargingcurrent (e.g., current source 352) and reset switch 353 are connected tothe analog mux bus. This may limit the pin-count requirement to simplythe number of switches (e.g., capacitors 351(1)-351(N)) to be addressed.In one exemplary embodiment, no external resistors or capacitors arerequired inside or outside the processing device 210 to enableoperation.

The capacitor charging current for the relaxation oscillator 350 isgenerated in a register programmable current output DAC (also known asIDAC). Accordingly, the current source 352 is a current DAC or IDAC. TheIDAC output current may be set by an 8-bit value provided by theprocessing device 210, such as from the processing core 202. The 8-bitvalue may be stored in a register or in memory.

Estimating and measuring PCB capacitances may be difficult; theoscillator-reset time may add to the oscillator period (especially athigher frequencies); and there may be some variation to the magnitude ofthe DAC output current with operating frequency. Accordingly, theoptimum oscillation frequency and operating current for a particularswitch array may be determined to some degree by experimentation.

In many capacitive switch designs the two “plates” (e.g., 301 and 302)of the sensing capacitor are actually adjacent PCB pads or traces, asindicated in FIG. 3A. Typically, one of these plates is grounded.Layouts for touch-sensor slider (e.g., linear slide switches) andtouch-sensor pad applications have switches that are immediatelyadjacent. In this case, all of the switches that are not active aregrounded through the GPIO 207 of the processing device 210 dedicated tothat pin. The actual capacitance between adjacent plates is small (Cp),but the capacitance of the active plate (and its PCB trace back to theprocessing device 210) to ground, when detecting the presence of theconductive object 303, may be considerably higher (Cp+Cf). Thecapacitance of two parallel plates is given by the following equation:

$\begin{matrix}{C = {{ɛ_{0} \cdot ɛ_{R} \cdot \frac{A}{d}} = {{ɛ_{R} \cdot 8.85 \cdot \frac{A}{d}}\mspace{20mu} p\; F\text{/}m}}} & (8)\end{matrix}$

The dimensions of equation (8) are in meters. This is a very simplemodel of the capacitance. The reality is that there are fringing effectsthat substantially increase the switch-to-ground (and PCBtrace-to-ground) capacitance.

Switch sensitivity (i.e., actuation distance) may be increased by one ormore of the following: 1) increasing board thickness to increase thedistance between the active switch and any parasitics; 2) minimizing PCtrace routing underneath switches; 3) utilizing a grided ground with 50%or less fill if use of a ground plane is absolutely necessary; 4)increasing the spacing between switch pads and any adjacent groundplane; 5) increasing pad area; 6) decreasing thickness of any insulatingoverlay; or 7) verifying that there is no air-gap between the PC padsurface and the touching finger.

There is some variation of switch sensitivity as a result ofenvironmental factors. A baseline update routine, which compensates forthis variation, may be provided in the high-level APIs.

Sliding switches are used for control requiring gradual adjustments.Examples include a lighting control (dimmer), volume control, graphicequalizer, and speed control. These switches are mechanically adjacentto one another. Actuation of one switch results in partial actuation ofphysically adjacent switches. The actual position in the sliding switchis found by computing the centroid location of the set of switchesactivated.

In applications for touch-sensor sliders (e.g., sliding switches) andtouch-sensor pads it is often necessary to determine finger (or othercapacitive object) position to more resolution than the native pitch ofthe individual switches. The contact area of a finger on a slidingswitch or a touch-pad is often larger than any single switch. In oneembodiment, in order to calculate the interpolated position using acentroid, the array is first scanned to verify that a given switchlocation is valid. The requirement is for some number of adjacent switchsignals to be above a noise threshold. When the strongest signal isfound, this signal and those immediately adjacent are used to compute acentroid:

$\begin{matrix}{{Centroid} = \frac{{n_{i - 1} \cdot ( {i - 1} )} + {n_{i}i} + {n_{i + 1} \cdot ( {i + 1} )}}{n_{i - 1} + {n_{i}i} + n_{i + 1}}} & (9)\end{matrix}$

The calculated value will almost certainly be fractional. In order toreport the centroid to a specific resolution, for example a range of 0to 100 for 12 switches, the centroid value may be multiplied by acalculated scalar. It may be more efficient to combine the interpolationand scaling operations into a single calculation and report this resultdirectly in the desired scale. This may be handled in the high-levelAPIs. Alternatively, other methods may be used to interpolate theposition of the conductive object.

A physical touchpad assembly is a multi-layered module to detect aconductive object. In one embodiment, the multi-layer stack-up of atouchpad assembly includes a PCB, an adhesive layer, and an overlay. ThePCB includes the processing device 210 and other components, such as theconnector to the host 250, necessary for operations for sensing thecapacitance. These components are on the non-sensing side of the PCB.The PCB also includes the sensor array on the opposite side, the sensingside of the PCB. Alternatively, other multi-layer stack-ups may be usedin the touchpad assembly.

The PCB may be made of standard materials, such as FR4 or Kapton™ (e.g.,flexible PCB). In either case, the processing device 210 may be attached(e.g., soldered) directly to the sensing PCB (e.g., attached to thenon-sensing side of the PCB). The PCB thickness varies depending onmultiple variables, including height restrictions and sensitivityrequirements. In one embodiment, the PCB thickness is at leastapproximately 0.3 millimeters (mm). Alternatively, the PCB may haveother thicknesses. It should be noted that thicker PCBs may yield betterresults. The PCB length and width is dependent on individual designrequirements for the device on which the sensing device is mounted, suchas a notebook or mobile handset.

The adhesive layer is directly on top of the PCB sensing array and isused to affix the overlay to the overall touchpad assembly. Typicalmaterial used for connecting the overlay to the PCB is non-conductiveadhesive such as 3M 467 or 468. In one exemplary embodiment, theadhesive thickness is approximately 0.05 mm. Alternatively, otherthicknesses may be used.

The overlay may be non-conductive material used to protect the PCBcircuitry to environmental elements and to insulate the user's finger(e.g., conductive object) from the circuitry. Overlay can be ABSplastic, polycarbonate, glass, or Mylar™. Alternatively, other materialsknown by those of ordinary skill in the art may be used. In oneexemplary embodiment, the overlay has a thickness of approximately 1.0mm. In another exemplary embodiment, the overlay thickness has athickness of approximately 2.0 mm. Alternatively, other thicknesses maybe used.

The sensor array may be a grid-like pattern of sensor elements (e.g.,capacitive elements) used in conjunction with the processing device 210to detect a presence of a conductive object, such as finger, to aresolution greater than that which is native. The touch-sensor padlayout pattern maximizes the area covered by conductive material, suchas copper, in relation to spaces necessary to define the rows andcolumns of the sensor array.

FIG. 5A illustrates a top-side view of one embodiment of a sensor arrayhaving a plurality of sensor elements for detecting a presence of aconductive object 303 on the sensor array 500 of a touch-sensor pad.Touch-sensor pad 220 includes a sensor array 500. Sensor array 500includes a plurality of rows 504(1)-504(N) and a plurality of columns505(1)-505(M), where N is a positive integer value representative of thenumber of rows and M is a positive integer value representative of thenumber of columns. Each row includes a plurality of sensor elements503(1)-503(K), where K is a positive integer value representative of thenumber of sensor elements in the row. Each column includes a pluralityof sensor elements 501(1)-501(L), where L is a positive integer valuerepresentative of the number of sensor elements in the column.Accordingly, sensor array is an N×M sensor matrix. The N×M sensormatrix, in conjunction with the processing device 210, is configured todetect a position of a presence of the conductive object 303 in the x-,and y-directions.

FIG. 5B illustrates a top-side view of one embodiment of a sensor arrayhaving a plurality of sensor elements for detecting a presence of aconductive object 303 on the sensor array 550 of a touch-sensor slider.Touch-sensor slider 230 includes a sensor array 550. Sensor array 550includes a plurality of columns 504(1)-504(M), where M is a positiveinteger value representative of the number of columns. Each columnincludes a plurality of sensor elements 501(1)-501(L), where L is apositive integer value representative of the number of sensor elementsin the column. Accordingly, sensor array is a 1×M sensor matrix. The 1×Msensor matrix, in conjunction with the processing device 210, isconfigured to detect a position of a presence of the conductive object303 in the x-direction. It should be noted that sensor array 500 may beconfigured to function as a touch-sensor slider 230.

Alternating columns in FIG. 5A correspond to x- and y-axis elements. They-axis sensor elements 503(1)-503(K) are illustrated as black diamondsin FIG. 5A, and the x-axis sensor elements 501(1)-501(L) are illustratedas white diamonds in FIG. 5A and FIG. 5B. It should be noted that othershapes may be used for the sensor elements. In another embodiment, thecolumns and row may include vertical and horizontal bars (e.g.,rectangular shaped bars), however, this design may include additionallayers in the PCB to allow the vertical and horizontal bars to bepositioned on the PCB so that they are not in contact with one another.

FIGS. 5C and 5D illustrate top-side and side views of one embodiment ofa two-layer touch-sensor pad. Touch-sensor pad, as illustrated in FIGS.5C and 5D, include the first two columns 505(1) and 505(2), and thefirst four rows 504(1)-504(4) of sensor array 500. The sensor elementsof the first column 501(1) are connected together in the top conductivelayer 575, illustrated as hashed diamond sensor elements andconnections. The diamond sensor elements of each column, in effect, forma chain of elements. The sensor elements of the second column 501(2) aresimilarly connected in the top conductive layer 575. The sensor elementsof the first row 504(1) are connected together in the bottom conductivelayer 575 using vias 577, illustrated as black diamond sensor elementsand connections. The diamond sensor elements of each row, in effect,form a chain of elements. The sensor elements of the second, third, andfourth rows 504(2)-504(4) are similarly connected in the bottomconductive layer 576.

As illustrated in FIG. 5D, the top conductive layer 575 includes thesensor elements for both the columns and the rows of the sensor array,as well as the connections between the sensor elements of the columns ofthe sensor array. The bottom conductive layer 576 includes theconductive paths that connect the sensor elements of the rows thatreside in the top conductive layer 575. The conductive paths between thesensor elements of the rows use vias 577 to connect to one another inthe bottom conductive layer 576. Vias 577 go from the top conductivelayer 575, through the dielectric layer 578, to the bottom conductivelayer 576. Coating layers 579 and 589 are applied to the surfacesopposite to the surfaces that are coupled to the dielectric layer 578 onboth the top and bottom conductive layers 575 and 576.

It should be noted that the present embodiments should not be limited toconnecting the sensor elements of the rows using vias to the bottomconductive layer 576, but may include connecting the sensor elements ofthe columns using vias to the bottom conductive layer 576.

When pins are not being sensed (only one pin is sensed at a time), theyare routed to ground. By surrounding the sensing device (e.g.,touch-sensor pad) with a ground plane, the exterior elements have thesame fringe capacitance to ground as the interior elements.

In one embodiment, an IC including the processing device 210 may bedirectly placed on the non-sensor side of the PCB. This placement doesnot necessary have to be in the center. The processing device IC is notrequired to have a specific set of dimensions for a touch-sensor pad,nor a certain number of pins. Alternatively, the IC may be placedsomewhere external to the PCB.

FIG. 6 illustrates a graph of one embodiment of a velocity of a presenceof a finger on a sensing device. Graph 600 includes the velocity of apresence of a conductive object 303 (e.g., finger) on sensing device 610as the conductive object 303 is substantially in contact with thesensing device 610 and when the conductive object 303 is notsubstantially in contact with the sensing device 610. As the conductiveobject 303 approaches the sensing device 610, the processing device 210detects the presence of the conductive object 303. The processing device210 determines the velocity of the presence of the conductive object 303as the conductive object 303 becomes substantially in contact with thesensing device 610, as illustrated by a first peak 603 in the velocityat a first time 601. The processing device 210 determines the velocityof the presence of the conductive object 303 as the conductive object303 becomes substantially not in contact with the sensing device 610, asillustrated by a second peak 604 in the velocity at a second time 602.Processing device 210 determines characteristics of each peak, such asheight of the peak, width of the peak, and time 601 of the peak. Usingthe height and width of the peak, a sharpness factor is determined. Thefirst peak 603 has a sharpness factor (Q1) 605, and the second peak 604has a sharpness factor (Q2) 606. The sharpness factors Q1 and Q2 arecompared against a sharpness threshold to determine if a peak isdetected. For example, if Q1 is greater than the sharpness threshold,then the first peak 603 is detected as the velocity of the conductiveobject 303 in a positive direction (e.g., towards the sensing device610), meaning the processing device 210 has detected the presence of theconductive object 303 as it becomes in substantial contact with thesensing device 610. Similarly, the processing device 210 detects thesecond peak 604 as the velocity of the conductive object 303 in anegative direction (e.g., away from the sensing device 610). Once theprocessing device 210 has detected the first and second peaks 603 and604, the processing device 210 determines the time difference T_(d) 607between the first time 601 and the second time 602. The processingdevice 210 recognizes a tap gesture based on the determined velocity. Inparticular, the tap gesture is recognized when the time differencebetween the first time 601 and the second time 602 is less than a timethreshold. The time threshold may be a preset static value, oralternatively, may be programmed by the user. Sensing device 610 may bea touch-sensor pad, a touch-sensor slider, or a touch-sensor button.

FIG. 7A illustrates a graph of one embodiment of a differential of thecapacitance over time on a sensing device. Graph 700 includes thecapacitance 708 of a conductive object 303 (e.g., finger) on sensingdevice 610 as the conductive object 303 is substantially in contact withthe sensing device 610 and when the conductive object 303 is notsubstantially in contact with the sensing device 610. As the conductiveobject 303 approaches the sensing device 610, the processing device 210detects the presence of the conductive object 303 by determining thecapacitance 708 of the conductive object 303. Although the graph isrepresentative of the differential of the capacitance over time, forillustration and description purpose, the capacitance 708 has beenillustrated along with the differential 709 of the capacitance 708. Theprocessing device 210 determines the differential 709 of the capacitance708 over time. The differential 709 is representative of the velocity ofthe presence of the conductive object 303 as the conductive object 303becomes substantially in contact with the sensing device 610, asillustrated by a first peak 703 in capacitance 708 at a first time 701.The processing device 210 determines the velocity of the presence of theconductive object 303 as the conductive object 303 becomes substantiallynot in contact with the sensing device 610, as illustrated by a secondpeak 704 in capacitance 708 at a second time 702. The first peak 701 isrepresentative of a rising edge of the capacitance 708 in a positivedirection, and the second peak 702 is representative of a falling edgeof the capacitance 708 in a negative direction.

Processing device 210 determines characteristics of each peak, such asheight of the peak, width of the peak, and time 601 of the peak. Usingthe height and width of the peak, a sharpness factor is determined. Thefirst peak 703 has a sharpness factor (Q1) 705, and the second peak 704has a sharpness factor (Q2) 706. The sharpness factors Q1 and Q2 arecompared against a sharpness threshold to determine if a peak isdetected. For example, if Q1 is greater than the sharpness threshold,then the first peak 703 is detected as the differential 709 of theconductive object 303 in a positive direction (e.g., towards the sensingdevice 610), meaning the processing device 210 has detected the presenceof the conductive object 303 as it becomes in substantial contact withthe sensing device 610. Similarly, the processing device 210 detects thesecond peak 704 as the differential 709 of the conductive object 303 ina negative direction (e.g., away from the sensing device 610).

Once the processing device 210 has detected the first and second peaks703 and 704, the processing device 210 determines the time differenceT_(d) 707 between the first time 701 and the second time 702. Theprocessing device 210 recognizes a tap gesture based on the determineddifferential 709. In particular, the tap gesture is recognized when thetime difference between the first time 701 and the second time 702 isless than a time threshold. The time threshold may be a preset staticvalue, or alternatively, may be programmed by the user.

Each sensor element outputs its own capacitance, however, when theconductive object 303 touches the sensing device 610, for example, atouch-sensor pad, some of the sensor element's capacitance increases,while other's capacitance do not increase. In one embodiment todetermine the capacitance 708, processing device 210 determines acapacitance of each of the sensor elements of the sensing device 610,and determines an average capacitance based on the capacitance of eachof the sensor elements. In another embodiment to determine thecapacitance 708, processing device 210 determines a capacitance of eachof the sensor elements of the sensing device 610, and determines whichsensor element has the largest difference in capacitance to determinethe capacitance 708. For both embodiments, once the capacitance isdetermined, processing device 210 determines the differential 709 of thecapacitance 708 to recognize whether or not a tap gesture has occurred.Alternatively, other methods known by those of ordinary skill in the artmay be used to determine the capacitance 708.

In one exemplary embodiment, the processing device 210 records thecapacitance of each sensor element in a scan loop. After finishing thescan loop, the processing device 210 calculates the differential of thesensor's capacitance. The processing device 210 selects the sensorelement, which has the biggest differential, and calculates itssharpness factor (Q), including its height and width of the peak, andthe time of each peak. The processing device 210 recognizes the tapgesture if the sharpness factors of the two peaks are greater than thethreshold sharpness factor, and if the time difference between the twopeaks is less than the time threshold.

In another exemplary embodiment, the processing device 210 records thecapacitance of each sensor element in a scan loop. After finishing thescan loop, processing device 210 adds up the capacitance of all of thesensor elements. After the processing device 210 sums the capacitance,it determines the differential of the summed capacitance, and calculatesits sharpness factor (Q), including its height and width of the peak,and the time of each peak. The processing device 210 recognizes the tapgesture if the sharpness factors of the two peaks are greater than thethreshold sharpness factor, and if the time difference between the twopeaks is less than the time threshold. Because the conductive object issubstantially in contact with the sensing device, wherever the presenceof the conductive object is detected, the summation of the capacitanceof all the sensor elements vary, in almost, if not exactly, the samemanner as that of the single contacting point (e.g., the selected sensorelement having the biggest difference). One advantage of this embodimentmay include reducing processing time needed to determine thecapacitance, and the differential of the capacitance.

It should be noted that embodiments described herein determine therising and falling edges of the capacitance of the sensing device,unlike the conventional sensing devices, which determine the timebetween two cross-points at a threshold level. As previously described,the differential of the capacitance over time naturally captures therising and falling edges of the capacitance, which represents thevelocity of the presence of the conductive object. The rising andfalling edges of the capacitance also represent the on- and off-actionsof the tap gesture. The peaks in the differential yield more informationabout the velocity of the presence, such as the sharpness of the peak.For example, a fast touch results in a sharper peak, than a slower touchaction. By using the sharpness of the peaks in the differential, theprocessing device 210 is operable to distinguish between tap gesturesand other non-tap gestures, such as slow touching.

FIG. 7B illustrates a graph of one embodiment of a peak in thedifferential of the capacitance on the sensing device. As previouslydescribed the processing device 210 determines characteristics of eachpeak, such as height of the peak, width of the peak, and time of thepeak. Graph 750 includes a peak 710 of the differential capacitance ofthe capacitance determined on the sensing device 610 (e.g., either onone sensor element or on all the sensor elements, as previouslydescribed). Processing device 210 determines a sharpness factor (Q) 713using the height 711 and the width 712 of the peak 710.

In one embodiment, the sharpness factor (Q) 713 is determined bydividing the height 711 by the width 712. Alternatively, other methodsknown by those of ordinary skill in the art may be used to determine thesharpness factor (Q) 713. The height 711 may be determined bydetermining the maximum height of the peak 710. Alternatively, othermethods known by those of ordinary skill in the art may be used todetermine the height 711 of the peak 710. The width 712 may bedetermined by determining the midpoint height of the peak 710, and atthat point determining the time difference between the two cross-pointsat that determined midpoint height. Alternatively, other methods knownby those of ordinary skill in the art may be used to determine the width712 of the peak 710.

It should be noted that the operations of processing device 210,described with respect to FIGS. 6, 7A, and 7B, may also be performed bya processing device of the host 250 (e.g., host processor), drivers ofthe host 250, the embedded controller 260, or by hardware, software,and/or firmware of other processing devices. For example, raw data fromthe sensing device may be sent to a processor, and the processor isconfigured to determine the velocity of the presence of the conductiveobject 303, to determine characteristics of each peak, such as height ofthe peak, width of the peak, and time of the peak. Similarly, theprocessor may be configured to determine the capacitance on the sensingdevice, determine the differential of the capacitance, detect first andsecond peaks in the differential, determine the time difference betweenthe two peaks, and/or recognize a tap gesture based on the data sentfrom the sensing device.

FIG. 8A illustrates a graph of one embodiment of an integration of thecapacitance over time on a sensing device. Graph 800 includes thecapacitance 808 of a conductive object 303 (e.g., finger) on sensingdevice 610 as the conductive object 303 is substantially in contact withthe sensing device 610 and when the conductive object 303 is notsubstantially in contact with the sensing device 610. As the conductiveobject 303 approaches the sensing device 610, the processing device 210detects the presence of the conductive object 303 by determining thecapacitance 808 of the conductive object 303. The processing device 210determines the integration 809 of the capacitance 808 between two pointsin time. In particular, the integration 809 is the integration ofcapacitance 808 between the two cross-points at a first time 801 and asecond time 802, at which the capacitance crosses the threshold valueC_(Th) 810. Processing device 210 may also calculate the time differenceT_(i) 807 between the first and second times 801 and 802 of the twocross-points. By integrating the capacitance 808, the processing device210 determines integration 809. Integration 809 is representative of thearea under the curve of the capacitance 808 and above the thresholdcapacitance C_(Th) 810. The processing device 210 recognizes a tapgesture based on the determined integration 809. In particular, the tapgesture is recognized when the integration 809 (e.g., area A) is abovean area threshold. The area threshold may be a preset static value, oralternatively, may be programmed by the user. This embodiment may havethe disadvantage of losing too much timing information. This may resultin incorrectly recognizing a tap gesture in certain situations, Forexample, the capacitance may slightly cross the threshold capacitanceC_(Th) 810, but do so for a long enough time to make the area largerthan the area threshold, incorrectly resulting in recognition of a tapgesture. This example is illustrated in FIG. 8B.

FIG. 8B illustrates a graph of another embodiment of an integration ofthe capacitance over time on a sensing device. Graph 850 includes thecapacitance 808 of a conductive object 303 (e.g., finger) on sensingdevice 610 as the conductive object 303 is substantially in contact withthe sensing device 610 and when the conductive object 303 is notsubstantially in contact with the sensing device 610. Like the exampleof FIG. 8A, the processing device 210 determines the integration 811 ofthe capacitance 808 between two points in time. In particular, theintegration 811 is the integration of capacitance 808 between the twocross-points at a first time 801 and a second time 802, at which thecapacitance crosses the threshold value C_(Th) 810. Processing device210 may also calculate the time difference T_(i) 807 between the firstand second times 801 and 802 of the two cross-points. By integrating thecapacitance 808, the processing device 210 determines integration 809.Integration 809 is representative of the area under the curve of thecapacitance 808 and above the threshold capacitance C_(Th) 810. Theprocessing device 210 recognizes a tap gesture based on the determinedintegration 811. In particular, the tap gesture is recognized when theintegration 811 (e.g., area B) is above an area or integrationthreshold. The area threshold may be a preset static value, oralternatively, may be programmed by the user. As previously described,this embodiment may have the disadvantage of losing too much timinginformation, and result in incorrectly recognizing a tap gesture.

In another embodiment, processing device 210, in addition to determiningthe integration 809 and comparing the integration 809 to the areathreshold, determines the time difference T_(i) 807 between the twocross-points at the first and second times 801 and 802. The processingdevice 210 recognizes a tap gesture based on the determined integration809 and the time difference T_(i) 807. In particular, the tap gesture isrecognized when the integration 809 (e.g., area A) is above an areathreshold and the time difference T_(i) 807 is less than a timethreshold. Using both these conditions, the processing device 210 doesnot incorrectly recognize a tap gesture in the example illustrated inFIG. 8B, because the time difference T_(i) 807 is greater than the timethreshold; even though the integration 808 (e.g., area B) is greaterthan the area threshold. Like the embodiments of determining thedifferential, the embodiments of determining the integration may includedetermining the integration based on the capacitance of the selectedsensor element, or the average capacitance of all the sensor elements.

It should be noted that the operations of processing device 210described with respect to FIGS. 8A and 8B, may also be performed by aprocessing device of the host 250 (e.g., host processor), drivers of thehost 250, the embedded controller 260, or by other processing devices,as described above with respect to FIGS. 6, 7A and 7B.

FIG. 9A illustrates a flowchart of one embodiment of a method forrecognizing a tap gesture on a sensing device. Method 900 includes,first, detecting a presence of a conductive object on a sensing device,operation 901; second, determining a velocity of the detected presenceof the conductive object, operation 902, and third, recognizing a tapgesture based on the velocity, operation 903. Determining a velocity ofthe detected presence of operation 902 may include determining acapacitance of the conductive object on the sensing device over time,and determining a differential of the capacitance over the time. Thedifferential is representative of the velocity of the presence of theconductive object. Recognizing the tap gesture of operation 903 includesrecognizing the tap gesture based on the differential. In particular,two peaks of the differential may be detected, and the time between thetwo peaks may be determined in order to recognize a tap gesture.

FIG. 9B illustrates a flowchart of another exemplary embodiment of amethod for recognizing a tap gesture on a sensing device 610. Method 950includes measuring an average capacitance of the whole sensing device610 (e.g., touchpad), operation 905. This is performed using thecapacitance sensor 201 and the sensing device 610. Next, the processingdevice 210 calculates the differential coefficient of the capacitance,operation 906. Next, the processing device 210 determines if thedifferential coefficient is less than a positive threshold, operation907. If the differential coefficient is less than the positivethreshold, the method goes back to repeat operations 905-907. If thedifferential coefficient is greater than the positive threshold, themethod goes to operation 908-910, which includes measuring the averagecapacitance of the whole sensing device 610 (operation 908), calculatingthe differential coefficient of the capacitance (operation 909), anddetermining whether the differential coefficient is greater than thepositive threshold (operation 910). If the differential coefficient isgreater than the positive threshold, the method goes back to operation908 and repeats operations 908-910. When the differential coefficient isless than the positive threshold, the method goes to operation 911,which includes calculating the sharpness factor (Q). This is performedby the processing core 202 of the processing device 210. The processingdevice 210 then determines whether the sharpness factor (Q) is greaterthan the sharpness factor threshold (Q Threshold), operation 912. If thesharpness factor (Q) is less than the sharpness factor threshold, thenthe determined differential is not a detected peak, operation 913.However, if the processing device 210 determines that the sharpnessfactor (Q) is greater than the sharpness factor threshold (Q Threshold)in operation 912, a positive peak for the differential is detected,operation 914. Detecting a positive peak indicates that a rising edge ofthe capacitance was detected by the processing device 210.

Next, the method includes measuring the average capacitance of the wholesensing device 610, operation 915. This is performed using thecapacitance sensor 201 and the sensing device 610. Next, the processingdevice 210 calculates the differential coefficient of the capacitance,operation 916. Next, the processing device 210 determines if thedifferential coefficient is greater than a negative threshold, operation917. If the differential coefficient is greater than the negativethreshold, the method goes back to repeat operations 915-917. If thedifferential coefficient is less than the negative threshold, the methodgoes to operation 918-920, which includes measuring the averagecapacitance of the whole sensing device 610 (operation 918), calculatingthe differential coefficient of the capacitance (operation 909), anddetermining whether the differential coefficient is less than thenegative threshold (operation 920). If the differential coefficient isless than the negative threshold, the method goes back to operation 918and repeats operations 918-920. When the differential coefficient isgreater than the negative threshold, the method goes to operation 921,which includes calculating the sharpness factor (Q). This is performedby the processing core 202 of the processing device 210. The processingdevice 210 then determines whether the sharpness factor (Q) is greaterthan the sharpness factor threshold (Q Threshold), operation 922. If thesharpness factor (Q) is less than the sharpness factor threshold, thenthe determined differential is not a detected peak, operation 923.However, if the processing device 210 determines that the sharpnessfactor (Q) is greater than the sharpness factor threshold (Q Threshold)in operation 922, a negative peak for the differential is detected,operation 924. Detecting a negative peak indicates that a falling edgeof the capacitance was detected by the processing device 210.

Next, the method includes calculating the time difference between thepositive and negative peaks, operation 925. This may also be performedby the processing core 202 of the processing device 210. Next, theprocessing device 210 determines whether the time difference is lessthan a time threshold, operation 926. If the time difference is lessthan the time threshold, the processing device 210 recognizes a tapgesture, operation 927. If the time difference is greater than the timethreshold, the processing device 210 does not recognize a tap gesture,operation 928.

Embodiments of the present invention, described herein, include variousoperations. These operations may be performed by hardware components,software, firmware, or a combination thereof. As used herein, the term“coupled to” may mean coupled directly or indirectly through one or moreintervening components. Any of the signals provided over various busesdescribed herein may be time multiplexed with other signals and providedover one or more common buses. Additionally, the interconnection betweencircuit components or blocks may be shown as buses or as single signallines. Each of the buses may alternatively be one or more single signallines and each of the single signal lines may alternatively be buses.

Certain embodiments may be implemented as a computer program productthat may include instructions stored on a machine-readable medium. Theseinstructions may be used to program a general-purpose or special-purposeprocessor to perform the described operations. A machine-readable mediumincludes any mechanism for storing or transmitting information in a form(e.g., software, processing application) readable by a machine (e.g., acomputer). The machine-readable medium may include, but is not limitedto, magnetic storage medium (e.g., floppy diskette); optical storagemedium (e.g., CD-ROM); magneto-optical storage medium; read-only memory(ROM); random-access memory (RAM); erasable programmable memory (e.g.,EPROM and EEPROM); flash memory; electrical, optical, acoustical, orother form of propagated signal (e.g., carrier waves, infrared signals,digital signals, etc.); or another type of medium suitable for storingelectronic instructions.

Additionally, some embodiments may be practiced in distributed computingenvironments where the machine-readable medium is stored on and/orexecuted by more than one computer system. In addition, the informationtransferred between computer systems may either be pulled or pushedacross the communication medium connecting the computer systems.

Although the operations of the method(s) herein are shown and describedin a particular order, the order of the operations of each method may bealtered so that certain operations may be performed in an inverse orderor so that certain operation may be performed, at least in part,concurrently with other operations. In another embodiment, instructionsor sub-operations of distinct operations may be in an intermittentand/or alternating manner.

In the foregoing specification, the invention has been described withreference to specific exemplary embodiments thereof. It will, however,be evident that various modifications and changes may be made theretowithout departing from the broader spirit and scope of the invention asset forth in the appended claims. The specification and drawings are,accordingly, to be regarded in an illustrative sense rather than arestrictive sense.

What is claimed is:
 1. A method comprising: using a capacitive sensor,determining capacitance associated with a conductive object through acapacitive sensing surface, during a period of time, to detect apresence of the conductive object; determining a first velocity of thedetected presence in a first direction relative to the capacitivesensing surface; determining a second velocity of the detected presencein a second direction relative to the capacitive sensing surface;detecting a change in the first velocity in the first direction at afirst time; detecting a change in the second velocity in the seconddirection at a second time; and recognizing a user command based on adifference between the first time and the second time.
 2. The method ofclaim 1, wherein the first direction is towards the capacitive sensingsurface and the second direction is away from the capacitive sensingsurface.
 3. The method of claim 1, wherein the detecting of the changein the first velocity in the first direction includes detecting a peakin the first velocity in the first direction and the detecting of thechange in the second velocity in the second direction includes detectinga peak in the second velocity in the second direction.
 4. The method ofclaim 3, wherein detecting the peak in the first velocity in the firstdirection and detecting the peak in the second velocity in the seconddirection comprises: determining a first sharpness factor of the changein the first velocity in the first direction based on a height and widthassociated with the change in the first velocity in the first direction;determining a second sharpness factor of the change in the secondvelocity in the second direction based on a height and width associatedwith the change in the second velocity in the second direction;detecting the peak in the first velocity in the first direction based oncomparing the first sharpness factor to a sharpness threshold; anddetecting the peak in the second velocity in the second direction basedon comparing the second sharpness factor to the sharpness threshold. 5.The method of claim 1, wherein the recognizing of the user command basedon the difference between the first time and the second time includesrecognizing the user command based on comparing the difference betweenthe first time and the second time to a threshold.
 6. The method ofclaim 1, wherein determining the first velocity and the second velocityof the detected presence comprises determining rate of change of thecapacitance, during the period of time, wherein the rate of change isrepresentative of the first velocity and the second velocity of thedetected presence.
 7. The method of claim 6, wherein detecting thechange in the first velocity in the first direction at the first timecomprises detecting a first peak of the rate of change of thecapacitance at the first time, and detecting the change in the secondvelocity in the second direction comprises detecting a second peak ofthe rate of change of the capacitance at the second time.
 8. The methodof claim 7, wherein the detecting of the first peak of the rate ofchange at the first time indicates a rising edge of the determinedcapacitance and the detecting of the second peak of the rate of changeat the second time indicates a falling edge of the determinedcapacitance.
 9. An apparatus comprising: a plurality of capacitivesensor elements; and a processing device coupled to the plurality ofcapacitive sensing elements, wherein the processing device is configuredto: determine capacitance associated with a conductive object throughthe plurality of capacitive sensor elements, during a period of time todetect presence of the conductive object relative to the plurality ofcapacitive sensing elements; determine first velocity of the detectedpresence in a first direction relative to the plurality of capacitivesensor elements; determine second velocity of the detected presence in asecond direction relative to the capacitive sensor elements; detect achange in the first velocity in the first direction at a first time;detect a change in the second velocity in the second direction at asecond time; and recognize a user command based on a difference betweenthe first time and the second time.
 10. The apparatus of claim 9,wherein the first direction is towards the capacitive sensing surfaceand the second direction is away from the capacitive sensing surface.11. The apparatus of claim 9, wherein the change in the first velocityin the first direction includes a peak in the first velocity in thefirst direction and the change in the second velocity in the seconddirection includes a peak in the second velocity in the seconddirection.
 12. The apparatus of claim 11, wherein the processing deviceis configured to determine a first sharpness factor of the change in thefirst velocity in the first direction based on a height and widthassociated with the change in the first velocity in the first direction,determine a second sharpness factor of the change in the second velocityin the second direction based on a height and width associated with thechange in second velocity in the second direction, detect the peak inthe first velocity in the first direction based on comparing the firstsharpness factor to a sharpness threshold, and detect the peak in thesecond velocity in the second direction based on comparing the secondsharpness factor to the sharpness threshold.
 13. The apparatus of claim9, wherein the processing device is configured to recognize the usercommand based on comparing the difference between the first time and thesecond time to a threshold.
 14. The apparatus of claim 9, wherein theprocessing device is configured to determine rate of change of thecapacitance wherein the rate of change is representative of the firstvelocity and the second velocity of the detected presence.
 15. Theapparatus of claim 14, wherein the processing device is configured todetect the change in the first velocity in the first direction at thefirst time as a first peak of the rate of change of the capacitance atthe first time, and detect the change in the second velocity in thesecond direction as a second peak of the rate of change of thecapacitance at the second time.
 16. The apparatus of claim 15, whereinthe first peak of the rate of change at the first time indicates arising edge of the determined capacitance and the second peak of therate of change at the second time indicates a falling edge of thedetermined capacitance.
 17. A system comprising: a touch input surfaceincluding a plurality of capacitive sensor elements; a processing devicecoupled to the touch input surface, wherein the processing device isconfigured to detect presence of an input object relative to the touchinput surface, determine first velocity of the detected presence in afirst direction relative to the touch input surface, determine secondvelocity of the detected presence in a second direction relative to thetouch input surface, detect a change in the first velocity in the firstdirection at a first time, detect a change in the second velocity in thesecond direction at a second time, and recognize a user command based ona difference between the first time and the second time; and a hostsystem coupled to the processing device, the host system configured usethe recognized user command in an operation of the host system.
 18. Thesystem of claim 17, wherein the processing device is configured tomeasure a capacitance associated with the input object through the oneor more of the plurality of capacitive sensor elements and determine arate of change of the capacitance signal, wherein the rate of change ofthe capacitance reflects the first velocity and the second velocity ofthe detected presence.
 19. The system of claim 18, wherein theprocessing device is configured to detect a first peak of the rate ofchange at the first time, detect a second peak of the rate of change atthe second time, determine a difference between the first time and thesecond time, and recognize the user gesture based on a comparisonbetween the determined difference and a threshold, wherein the usercommand includes a touch gesture.
 20. The apparatus of claim 17, whereinthe first direction is towards the capacitive sensing surface and thesecond direction is away from the capacitive sensing surface.